The invention relates to an oil pump of the vane type which can, for example, be used in a power steering apparatus utilized to facilitate handling of a steering wheel of an automobile.
An oil pump of this kind generally comprises a rotor having a plurality of radially extending slits in which a plurality of vanes are slidably assembled, a cam ring having a cam surface of substantially elliptical form and disposed in surrounding relationship with the rotor, and a sideplate and a pressure plate disposed on the opposite sides of the combination of the rotor and the cam ring to define a pump chamber together with the cam ring. As the rotor rotates, the vanes disposed in the slits move in a reciprocating manner, with their outer ends disposed in sliding contact with the cam surface to provide a pumping function. An oil pump of the vane type permits its operation at a reduced noise level while utilizing a relatively simple construction and presents a high operational reliability and freedom from failures. Because of these advantages, it finds an extensive application in a variety of fields.
In the conventional construction of such an oil pump, the components of the pump including the rotor, the cam ring, the sideplate and the pressure plate are disposed in a space defined within a pump body, through which a rotary shaft of the rotor extends and is rotatably journaled. This increases the overall length and the outer diameter as well as the weight of the pump. In addition, it requires an increased number of parts, many of which must be machined in a troublesome operation. All of these factors contribute to increasing the manufacturing cost of the pump.
It should be noted that the problem is even more aggravated if a flow control valve controlling the flow rate of an operating or hydraulic oil discharged from the pump chamber and a relief valve which maintains the oil pressure below a given value must be integrally disposed within the pump body, as required in an oil pump which is used in a power steering apparatus, for example. Specifically, if the flow control valve and the relief valve are integrally mounted on the pump in surrounding relationship or laterally of the pump components, the outer diameter or the overall length of the pump body will further increase. Such result is particularly notable in many oil pump arrangements having a relief valve which is assembled into a flow control valve, thus presenting an increased overall length of the valve.
On the other hand, an oil pump of the type which is utilized in a power steering apparatus is subject to a number of limitations in view of the limited space available within an engine compartment and the desirability of reducing its influence upon the entire weight and the cost of an automobile. Therefore, it is apparent that there has been a need in the art to eliminate the described difficulties by providing an oil pump which is small in size and low in weight and inexpensive to manufacture.